Study of the Transients of Loss of Coolant Accident in an Installation Pressurized with the RELAP5/mod3.2 System Code

摘要

This study consists of the simulation of a number of thermal-hydraulic transients, like the LOCA (Loss Of Coolant Accident), that can occur during the operation of a highly pressurized test loop, under saturation conditions. The loop is intended mainly for the tests of irradiations of nuclear fuel under high pressure and high temperature conditions (155 bars, 300 deg C). Three test sections (IPS), provided each one with an assembly with nine combustible bars, are conceived for this purpose. The primary cooling system is composed of a heat exchanger, a pressurizer and three test sections, in addition to the connecting pipe and sets of valves for regulate the flows. The RELAP5 code (Reactor Excursion and Leak Analysis Program) is a system code, broadly known, conceived for the simulation of the thermal-hydraulic behaviour of nuclear and non-nuclear installations. Our work, concerns two transients of loss of coolant accident in the primary cooling system. There is a whole spectrum of possible breaks of the primary cooling system, beginning with those which are sufficiently small so that the escapes are compensated by the flow of load of the volumetric and chemical checking loop, until the complete break of a principal pipe of the primary cooling system, accompanied by complete separation and double ended guillotine pipe break. This last rupture can be supposed to occur on the level of: the hot branch, between the section of tests and the heat exchanger, the intermediate branch, between the heat exchanger and the primary pump, and finally, the cold branch, between the pump and the test sections, at the return towards the core of the test sections (I.P.S). The spectrum of this type of breaks and their various localizations, deserve to be studied, because the physical and mechanical phenomena as well as the behaviour of the systems of safeguard (safety and control) vary from one case to another. In this article, we present the principal results of the analysis of two LOCA accidents simulated with RELAP5/MOD3.2 code.